Allelic deletions of 18q affect 90 percent of pancreatic cancers, but the target was unknown. The mapping of homozygous deletions, assembled as preliminary data for this grant application, uncovered a novel gene, DPC4. Initial studies showed that at least half of pancreatic cancers harbor inactivating genetic alterations of DPC4. DPC4 was homozygously deleted in 30 percent of pancreatic tumors. Point mutations that would cause gross disruption or malfunction of the gene product were seen in nearly a quarter of additional pancreatic tumors. Other tumor systems appear to have a lower rate of DPC4 mutation than that found in pancreatic cancer. DPC4 has no recognizable peptide motifs, but the function of DPC4 was suggested by strong sequence similarities to Drosophila and C. elegans genes involved in TGF-beta superfamily pathways. The studies outliend in this proposal will extend these results at the 18q homozygous deletion site. They will: 1) Determine the gene structure and genetic alterations of DPC4. This will include cloning of the non-coding regions, determination of regions of evolutionary conservation, and the comparison of mutations in pancreatic and other human tumor types. 2) Determine the expression patterns and biochemical interactions of DPC4 gene products. This will include the development of antibodies, the patterns of DPC4 expression in developing, adult, and neoplastic tissues, the exploration of various biochemical properties, and the identification of interacting proteins. 3) Analyze the biological function of DPC4 in normal, engineered, and cancer cells. This will include the manipulation of DPC4 expression in various cell types, observation of phenotypic effects, and the evaluation of responsiveness to TGF-beta superfamily members. A knockout mouse model will be developed, and murine and human cells having differing DPC4 genotypes will be compared.